Optical discs are one type of recording media used to store a wide variety of digitally encoded data. Such discs are usually portable in nature and can be played in a variety of settings.
A typical optical disc comprises a circular disc having one or more recording layers of light reflective material embedded in a refractive substrate. Each recording layer records data along a series of concentric tracks (such as discrete closed tracks or along a continuous spiral).
A data transducing head uses a laser or similar light source to output a readback signal based on the different reflectivities of areas along the tracks. Decoding circuitry decodes the user data for output by the appropriate playback device. Optical discs can be pre-recorded (pressed) replica discs, or can be written by the end user (e.g., recordable—write once; re-writable—write many).
Both pre-recorded and writable discs are often manufactured using one or more stampers, which in turn are created during a mastering process utilizing a laser beam recorder (LBR). In order for the optical discs to have optimal readability, it is desirable to measure and confirm various parameters to be within the associated specifications for such discs. One such parameter is track pitch.
Track pitch can be defined as the radial separation distance between the centerlines of immediately adjacent tracks, whether closed discrete concentric tracks or tracks within a continuous spiral. Some formats of optical discs (such as compact discs, CDs, and digital versatile discs, DVDs) specify a constant track pitch from lead-in to lead-out. Other formats of optical discs (such as high density DVD, HD-DVD, and Blu-Ray Discs, BDs) specify different track pitches at different locations within the recording layers.
Prior art methodologies for obtaining individual track pitch measurements on a recording medium have generally been difficult to carry out, and have sometimes included the use of expensive and cumbersome equipment such as laser inferometers and atomic force microscopes (AFMs). Accordingly, there remains a continued need for advancements in the art in the manner in which the track pitch between adjacent tracks on a recording medium such as an optical disc can be readily and accurately determined. It is to this and other needs that the present invention is generally directed.